| Abstrakt: |
Production data from a 5-year study with Angus × Hereford and Hereford cows that calved each year were analyzed for determination of the effects of breed of dam, breeding season, supplementation, year and their possible interactions on calf birth date, branding weight (≃ 60-day weight), 220-day weaning weight, gain from birth to weaning, cow efficiency and calving interval under New Mexico range conditions. Year affected all the traits, indicating the dependence of range cattle on climatic conditions. A drought in 1974 was especially detrimental to cow productivity. Calf gain from birth to weaning was 20% lower, adjusted weaning weight 17% lower and subsequent calving interval 16 days longer in 1974 than in the other years in the study. Interactions with significant effects were breed of dam X breeding season on calving interval, breeding season × supplementation on birth date and branding weight, and breeding season × year on branding weight. Calves from Angus X Hereford cows were heavier (P<.001) than those from Hereford cows at branding and weaning (82.1 vs71.3 kg and 223 vs205 kg, respectively). Also, Angus X Hereford cows were more efficient (P<.001) at weaning than Hereford cows (i.e., calf weaning weight made up a higher percentage of cow weight; 47.4 vs42.0%); and early-bred cows were more efficient (P<.05) than late-bred cows (46.4 vs43.0%). Calves from supplemented cows were heavier (P<.01) at weaning and gained more (P<.01) from birth to weaning than did those from unsupplemented cows (221 vs207 kg and .86 vs.80 kg/day, respectively). Supplemented cows had a shorter (P<.05) calving interval than unsupplemented cows (362.3 vs366.9 days). Three- and four-factor interactions were nonsignificant. |
